Sound and Music
Tips and tricks
The C64 can generate sound via its Sound Interface Device chip, referred to as the SID. The chip is a programmable synthesiser. It has a flexible programmable frequency, Attack, Release and Decay controling, filtering and mixing circuit. One can alter a rather great number of parameters, and by dynamically alteration of these parameters, it is possible to generate the rather sophisticated sound-effects, and music used in demos, games and intros etc. See the Programming section for more specific details about the SID registers, and the Hardware Architecture section for more about the chip itself.
The basic C64 (or C128) has a SID which has the feature seen in the scheme below, this is enough to make, for example the music which the computer is well-known for (Hmm, some talent is needed too) .
Features of the 6581/8580 Sound Interface Device
3 Tone Oscillators, Range 0-4kHz
4 waveforms per oscillator
Triangle, Sawtooth, Variable Pulse, Noise
3 Amplitude Modulators
Range 48 dB
3 Envelope Generators
Random Number/Modulation generator
Attack Rate: 2 ms - 8 s
Decay Rate: 6 ms - 24 s
Sustain Level: 0 - peak volume
External Audio Input
Release Rate: 6 ms - 24 s
Cutoff Range: 30Hz-12kHz
Master Volume Control
12 dB/octave Rolloff
2 A/D POT Interfaces
Low pass, Band pass, High pass, Notch outputs
Most people have the basic system, with only the normal SID, but expansions exists which takes the advantage of using two, or more SID chips. By combining several SID chips it is possible use more voices, and the possibility of stereo is present. However, just one SID can the programmed to do amazing things, and by using tricks one can have extra voices.
The SID chip became famous along with the C64, and the SID is now being used elsewhere, like in some special sound-cards (for PC) and professional studio equipment, MIDI slaves etc. All this is due to its very distinctive sound. It has gained alot of followers during the C64/128 area, and this also supports development of SID based devices for professional use.
SID emulators, making a sound rather close to the real SID, has made its way to the PC, and by using such, you can play some of the golden oldies (or new ones) on your PC.. There also exists an internet-browser SID web plugin, so you can you hear SID tunes placed on websites. See the ScLinx section where to get the stuff.
>> Under construction <<
Most musicians use some sort of composer or tracker software, a so called music-editor to assist them while making music, this is making it a much more comfortable process as they can focus on the sound and music, rather than the actual programming. In such software it is possible to write the sequences of alterations of the parameters in the SID to be performed, and make loops etc. Some editors can interpret different kinds of musical nodes etc. Depending of your choice of software, you have different options available, and you must learn its syntax and use.
Typically, the music is then saved along with an embedded player routine, which has only to be called once for initialisation and one or more times during screen refresh (The raster is widely used for timing all sorts of things on the C64). Different music editors is available, you have to decide which best suit your purpose, and which you like etc... The Init- and Play addresses can vary from player to player, and so can the raster time the player uses.
Some examples of music editors for making music (Just a small
handful, out of many):
AudioMaster - MSI (MegaStyle Inc.)
SID DUZZ `It
Music Assembler - Dutch USA-team
DMC (Demo Music Creator)
GMC (Game Music Creator)
Soundtracker 64 - Mechanix
JCH music editor - JCH/Vibrants (Jens Christian Huus)
Future Composer - by Finnish Gold
Soundmonitor - Chris Hülsbeck
PRO-Drum - Dutch USA-team
Rockmonitor - Dutch USA-team
Soedesoft Editor - Jeroen Soede
Some are old, like the classic Future Composer etc. and you might want a new editor, but it is all up to you. I am sure you can find some of these in one version or another, and/or similar music editors around.
"Knacks"and their application
Knacks are knickering sounds generated (by an error) in the SID chip when alternating the volume control. Only the 6581 versions (old SID) have this error to en extent where it has any pracical value.
The knacks makes it possible, under software control, to generate a sound which can the used for adding an extra sound channel to the SID. You can then have 3 voices + the knack channel. An application for this could be sound effects (while having music) or as an special voice in sound tracks. But since not all SID's has this, one could consider whatever this has any practical value. It has however been used in some software.
"HARD RESTART" on the 6581 SID version
A problem when it comes to the 6581 SID version is that the accuracy on Attack after releasing a note is rather bad. Two different solutions to this problem has been implemented some players, other players does not deal with the matter at all. Some players clears the SID registers (0-6) by writing $00 into all registers at $D400-D406, atleast 215 cycles before next Attack (in the ADSR cycle) (timer typically implemented as two frames before Attack). Other players sets the Test bit in the Voice Control Register (and thereby disables the Oscillator), and this is supposed to be enough. This technique is call "Hard Restart".
The problem does not seem to exist on the 8580 versions of the SID (However, the distinctice sound of the 6581 is preferred by many people - especially the implementation of the filters varies, that makes a change). In general one could say the 6581 is the soundchip of the C64 and the C128, while the 8580 is used in the later models of C64C and C128D.